The present invention is related generally to control circuits for radio frequency (RF) signal power amplifiers, and more particularly to improved automatic power output control circuitry for RF signal power amplifiers having a wide dynamic range.
Generally, radio frequency power amplifiers are operated at one output power level, and such power amplifiers are adjusted during manufacture to the desired output power level. In some applications, it has been desirable to have two power levels, a high and a low level. The RF signal power amplifier for such applications would have one setting for the high power level and another for the low power level. In many instances, these power amplifiers have control circuitry which prevents an excess of high applied voltage from the power supply, a large antenna mismatch, or an extreme of environment from destroying the active devices which comprise the power amplifier.
Recently, it has become advantageous to reuse radio channels in some radio communications systems. In order to avoid interference between two RF signal power amplifiers using the same frequency, it is desirable to have many different selectable output power levels, one of which is chosen for optimum communication efficiency of each RF signal power amplifier with a minimum of interference to other power amplifiers. For example, four power levels are available in the RF signal power amplifier employed in the mobile radio telephone described in Motorola instruction manual no. 68P81039E25, entitled "Advanced Mobile Phone System", and published by Motorola Service Publications, 1301 E. Algonquin Road, Schaumburg, Ill. 1979. The four power levels produced therein are achieved by varying reference voltage which is applied to an automatic output control circuit.
Additionally, RF power amplifier having eight power levels and an associated power control circuit has been disclosed in U.S. patent application No. 491,499 filed in behalf of Walczak et al. on May 4, 1983 and assigned to the assignee of the present invention. Since the absolute level of each of the eight power levels employed therein must be maintained relatively constant, the control circuitry must be temperature compensated to prevent drift of the power level of each power level over extremes of temperature. This temperature compensation has been achieved by the use of separate and discrete temperature compensating elements which add to the complexity of the control circuit.